Printing process and solder mask ink composition

ABSTRACT

A process for making an electronic device which comprises applying a non-aqueous solder mask ink which is substantially free from organic solvent to a dielectric substrate containing electrically conductive metal circuitry, exposing the solder mask ink to actinic radiation and/or particle beam radiation optionally followed by thermal treatment, whereby the solder mask ink is applied to selected areas of the substrate under the control of a computer by ink jet printing and wherein the solder mask ink comprises the components: A) 30-90 parts acrylate functional monomers which are mono or higher acrylate functional monomers comprising from 5-95% by weight of one or more monofunctional monomers; B) 0.1-30 parts metal adhesion promoting organic compound; C) 0-30 parts initiator, D) 0-10 parts polymer and/or prepolymer; E) 0-5 parts colorant; E) 0-5 parts surfactant; and Wherein all parts are by weight.

The present invention relates to a process for making Printed CircuitBoards (hereinafter PCB's) wherein the solder mask is applied to alaminate comprising a dielectric substrate having electricallyconductive metal circuitry and where the solder mask is applied by inkjet printing of a computer generated solder mask image.

In the conventional manufacture of PCB's a laminate comprising adielectric substrate having a copper sheet affixed to at least one sideis prepared. The copper surface is overlaid with a photo-resist layerwhich is typically a carboxylic acid containing polyacrylate. Aphototool is prepared which is a negative image of the desired copperelectrically conductive circuitry and this is typically a silver halidephotographic emulsion. The phototool is placed over the photo-resistlayer and irradiated with actinic radiation such as UV light. Thiscauses the photo-resist layer which is exposed to the actinic radiationto polymerise and harden thus producing a latent negative image of thedesired circuitry in the photo-resist layer. The unexposed areas of thephoto-resist layer which has not been exposed to actinic radiation isthen removed using mild aqueous alkali to expose the copper surface andthis is then removed by chemical etching resulting in a dielectricsubstrate containing the required copper circuitry covered bypolymerised photo-resist. This photo-resist is finally removed to give adielectric substrate having the required copper electrically conductivecircuitry.

PCB's are now complex sandwiches of numerous individual dielectricsubstrates containing copper electrically conductive circuitry on one orboth sides and the circuitry of these individual elements must beelectrically joined in a precise manner in forming the final PCB.

This is typically achieved by using a similar process to that used inpreparing the copper electrically conductive circuitry by thephoto-resist process described above. Thus, the individual elementscomprising a dielectric substrate containing the copper electricallyconductive circuitry is coated with a solder mask liquid film which isbased on acrylates having carboxylic acid groups. This solder mask filmis applied in such a manner to cover the copper circuitry and alsopenetrate between different tracks of the copper circuitry down to thesurface of the dielectric substrate itself. A phototool is preparedwhich is a negative image of those parts of the copper circuitry whichit is desired to join. This phototool is typically a silver halideemulsion which is similar to that used in the photo etch resistantpreparation of the electrically conductive copper circuitry. Thephototool is placed over the solder mask liquid film and irradiated withactinic radiation such as UV light. This causes the acrylate liquidsolder mask to polymerise and harden where it is exposed to actinicradiation. The unexposed areas of the solder mask are then removed usingdilute aqueous alkali thereby exposing those parts of the electricallyconductive copper circuitry which it Is desired to electrically join.The retained solder mask is generally further polymerised and hardenedby exposure to high temperatures, typically from 120 to 160° C. Theexposed copper surface is then coated with a liquid solder paste whichis held in place by the cured parts of the solder mask and heated tomelt the solder paste.

When the PCB is a sandwich containing two or more dielectric substrateswith copper electrically conductive circuitry the separate dielectricsubstrates are connected together by a dielectric prepeg which iscompatible with the substrate.

The solder mask also provides protection against heat, environmentaldamage and breakdown of the PCB during its life. Consequently, it iscommon to apply the solder mask also to the outer surface(s) of the PCB.

There are a number of deficiencies inherent in this process using soldermasks. It is a multi-stage process involving six discreet stages andrequires the separate preparation of a phototool. The liquid solder maskfilm is applied over the whole surface of the dielectric substratecontaining the required electrically conductive circuitry includingthose areas from which it is subsequently removed. This is wasteful ofmaterials. The phototool is distanced from the solder mask film andbecause of light diffraction some areas of the liquid solder mask whichare not directly beneath the exposed areas of the phototool tend topolymerise and are more difficult to remove by aqueous alkali. Thisadversely affects the definition and line density of those parts of thecopper circuitry it is desired to expose for contact with the solderpaste. Furthermore, use of solder mask acrylate polymers which need tobe quickly and effectively removed in a relatively short timeframerequires a relatively high carboxylic acid content. This can adverselyimpact on those parts of the solder mask which are retained forprotection of the individual elements of the PCB. A high number ofresidual carboxylic acid groups can also reduce the electricalsensitivity of the retained parts of the solder mask by conversion tothe salt of the carboxylic acid.

There is therefore a clear advantage in eliminating the need for aphototool and developing a process wherein the solder mask is applieddirectly to selected areas of a dielectric substrate by ink jet printingwhere the image is computer generated. This reduces the number ofprocessing stages since it is then only necessary to apply the soldermask to the required parts of the dielectric substrate containing thecopper circuitry and to polymerise the solder mask. Such a process saveson solder mask materials since it is only applied to those areas it isrequired to cover. It eliminates flow problems in applying liquid soldermask to the whole of the dielectric substrate containing the coppercircuitry where it is often difficult to avoid entrainment of airbetween adjacent copper tracks which can adversely effect PCBperformance and longevity. Since such a process does not involve aphototool which is distanced from the surface of the solder mask thereis no actinic radiation diffraction and polymerisation of the soldermark which is not directly below the transparent areas of the phototool.This offers the potential for greater definition and line density of thesolder paste. Because the solder mask is only applied to the requiredareas of the dielectric substrate containing the copper circuitry, it isnot necessary to selectively remove the solder mask from undesired areasby aqueous alkali treatment. The solder mask does not, therefore, needto have a high carboxylic acid content which offers the potential forimproved electrical resistance of the solder mask.

According to the present invention there is provided a process formaking an electronic device which comprises applying a non-aqueoussolder mask ink which is substantially free from organic solvent to adielectric substrate containing electrically conductive metal circuitry,exposing the solder mask ink to actinic radiation and/or particle beamradiation optionally followed by thermal treatment, whereby the soldermask ink is applied to selected areas of the substrate under the controlof a computer by ink jet printing and wherein the solder mask inkcomprises the components:

-   -   A) 30-90 parts acrylate functional monomers which are mono or        higher acrylate functional monomers comprising from 5-95% by        weight of one or more monofunctional monomers;    -   B) 0.1-30 parts metal adhesion promoting organic compound;    -   C) 0-30 parts initiator,    -   D) 0-10 parts polymer and/or prepolymer;    -   E) 0-5 parts colorant; and    -   F) 0-5 parts surfactant;        wherein all parts are by weight.

As disclosed hereinbefore the solder mask ink is substantially free oforganic solvents. By this is meant no additional solvents are requiredand only traces of solvents may be present as impurities or by-productsin the manufacture of the various components used to make the ink. It ispreferred that the ink contains not greater than 2 parts, morepreferably not greater than 1 part and especially not greater than 0.5parts organic solvent based on the total amount of the ink. It is mostpreferred that the solder mask ink is free from organic solvent.

The required viscosity of the solder mask ink is largely dependant onthe particular print head employed and especially its temperature ofoperation. At present most suitable commercial print heads operate at atemperature from 25° C. to 65° C. Consequently, it is preferred that theviscosity of the solder mask ink is not greater than 30 cPs (mPa.s) at40° C. Viscosity can be measured on any suitable equipment but ispreferably measured using a Brookfield viscometer with a rotatingspindle, for example a number 18 spindle. Preferably the viscosity ofthe solder mask is not greater than 20 and especially not greater than15 cPs (mPa.s) at 40° C. It is also preferred that the viscosity is notless than 5 and especially not less than 8 cPs (mPa.s) 40° C. Preferablythe viscosity is from 8 to 15 cPs (mPa.s) at 40° C. In one embodimentthe number of parts of components A)+B)+C)+D)+E)+F)=100.

Preferably the ink jet printing is carried out using a Drop-on-Demand(DOD) piezo ink jet printer.

The term acrylate-functional as used hereinbefore means any monomerwhich contains the residue of a reactive vinyl group such as CH₂═C(R)CO—where R is hydrogen alkyl or cyano. When R is alkyl it is preferablyC₁₋₆-alkyl. It is particularly preferred that the acrylate functionalityis conferred by a methacryloyl or especially an acryloyl group. Themonomers may have a relatively low molecular weight or they may beoligomeric or polymeric in nature and may be of a molecular weight ashigh as 30,000. They are distinguished from the polymers or prepolymerswhich is component D) of the ink composition in that they are notpolymers or prepolymers derived from the polymerisation of acrylatefunctional monomers. They may, however, be macromolecular and maycontain hydrocarbyl groups linked by one or more heteroatoms as forexample in polyethers, polyamides, urethanes, polyesters and ureas. Theonly limitation on the type and molecular size of the acrylatefunctional monomers is that they must be compatible, the one with theother, they must not form separate phases in the final solder mask ink,the solder mask ink must have the prescribed viscosity. Typically, theacrylate functional monomers have a weight average molecular weight (Mw)below 30,000, more preferably not greater than 10,000, even morepreferably not greater than 5,000 and especially not greater than 2,000since this helps keep the viscosity of the solder mask ink within theprescribed limits.

Specific examples of acrylate functional monomers are those which arecommercially available under the Sartomer™, Actilane™ and Photomer™trademarks such as Sartomer™ 506 (isobomyl acrylate), Sartomer™ 306(tripropylene glycol diacrylate), Actilane™ 430 (trimethylol propaneethoxylate triacrylate), Actilane™ 251 (a tri-functional acrylateoligmer), Actilane™ 411 (a CTF acrylate), Photomer™ 4072 (trimethylolpropane propoxylate triacrylate), Photomer™ 5429 (a polyester tetraacrylate) and Photomer™ 4039 (a phenol ethoxylate monoacrylate).Sartome™, Actilane™ and Photomer™ are trademarks of Cray Valley Inc,Akros BV and Cognis Inc, respectively. Other examples of monomers arelauryl acrylate, isodecylacrylate, iso-octyl acrylate, butyl acrylate,2-hydroxy ethyl acrylate, 2-hydroxy propylacrylate, 2-ethyl hexylacrylate, 1,6-hexanediol diacrylate, neopentyl glycol diacrylate,diethylene glycol diacrylate, butanediol diacrylate, trimethylolpropanetriacrylate, pentaerythritol triacrylate, 1,3-butylene glycoldiacrylate, 1,4-butylene glycol diacrylate, triethylene glycoldiacrylate, pentaerythritol tetra acrylate, tripropylene glycoldiacrylate, isobornyl acrylate, 2-norbornyl acrylate, cyclohexylacrylate, phenoxyethyl acrylate and tetrahydrofurfuryl acrylate.

Preferably the acrylate functional monomer is isobornyl acrylate,tripropylene glycol diacrylate or trimethylol propane ethoxylatetriacrylate.

It is preferred that the amount of mono-functional acrylate monomer is15-95%, more preferably 40-95%, especially 60-95% and more especially70-95% by weight of the total amount of acrylate functional monomersrepresented by component A).

The adhesion promoting organic compound may be any organic compoundwhich contains a metal chelant group or groups which can form a bondwith the metal forming the conductive circuitry of the electrical deviceand which is compatible with the acrylate functional monomers ofcomponent A). This is referred to hereinafter as Adhesion Promoter. TheAdhesion Promoter may be monomeric or polymeric in nature and maycontain one or more acrylate functional groups as defined hereinbefore.Where the Adhesion Promoter does not react with the acrylate-functionalmonomers of component A) it is preferably capable of intercolating withthe polymeric material formed by component A) after exposure to actinicradiation or particle beam radiation (e.g. electron beam) and optionallythermal treatment. However, it is preferred that the Adhesion Promoteris capable of reacting with the acrylate-functional monomers ofcomponent A) either during exposure to actinic radiation or particlebeam radiation or during subsequent thermal treatment. Whilst theAdhesion Promoter may contain any group capable of reacting with theacrylate functional monomers of component A), it is very much preferredthat the Adhesion Promoter is also acrylate-functional and especially anacrylate-functional monomer, e.g. (meth)acrylic acid.

The metal chelant group of the Adhesion Promoter is any organic moietywhich contains a hydrogen atom capable of being displaced by the metalof the electrically conductive circuitry or which possesses a lone pairof electrons capable of forming a bond with the said metal. Examples ofsuch groups are hydroxides, especially aryl or heteroaryl hydroxidessuch as phenolic hydroxides; amines which may be aliphatic, aryl orheteroaryl; mercaptans which may be aliphatic, aryl or heteroaryl;carboxylic acids which may be aliphatic, aryl or heteroaryl; oximes andketoximines; acetarylamides; hydroxy silanes and silicones; N-containingheterocyles such as imidazoles, benzimidazoles, triazoles,benztriazoles, thiazoles, isothiazoles and acid anhydrides. Where theAdhesion Promoter contains more than one metal chelant group these maybe the same or different. In one preferred class of Adhesion Promoterswhich contains two chelant groups, the chelant groups are attached toadjacent carbon atoms such as β-diketones, β-keto esters, β-ketoaldehydes and β-keto heterocyles.

Preferably the metal chelant group is carboxylic acid. Examples include2-acrylamido glycolic acid, mono-2-(methacryloyloxy)ethyl phthalate,acrylic acid, methacrylic acid, 2-carboxyethyl acrylate, 2-acetamidoacrylic acid, mono-2-(acryloyloxy)ethyl succinate,2,2-bis(acryloylamino)acetic acid, bis(2-(methacryloylethyl)phosphate,bis-(3-sulphopropyl)itaconic acid, ethylene glycol methacrylate,itaconic acid, mono-2-(methacryloyloxy)ethyl phosphate,mono-2-(methacryloyloxy)ethyl succinate, 2-(sulpho oxy)ethyl methacrylicacid, 2-acrylamido-2-methyl-1-propane sulphonic acid, 3-sulphopropylacrylic acid, mono-2-(methacryloyloxy)ethyl phthalate, 3-sulphopropylmethacrylic acid, maleic acid, fumeric acid andmono-2-(acryloyloxy)ethyl phthalate. Actilane™ 276 (tetra functionalurethane acrylate), Actilane™ 320 HD 20 (difunctional epoxy acrylate),Actilane™ 340 (trifunctional epoxy acrylate), Actilane™ 505(tetrafunctional polyester acrylate), MEM (acetoacetoxyethylmethacrylate), Photomer™ 5929 (polypropylene glycol tetraacrylate), Actilane™ 820 (difunctional acrylate), Actilane™ 872(difunctional acrylate), Actilane 890 (pentafunctional melamineacrylate), Photomer™ 5004F (silane acrylate), Sartomer™ 3050 (acidicmonoacrylate), mono-2-(methacryloyloxy)ethyl succinate,bis(2-methacryloxy)ethylphosphate, Photomer™ 4703, 2-hydroxy-3-phenoxypropyl acrylate and diurethane dimethacrylate. Actilane™, Photomer™ andSartomer™ are trade names of Akros BV, Cognis Inc and Cray Valley Inc,respectively. The precise chemical structure of those Adhesion Promotersavailable under commercial trade names is not known but from thedescription of the products they are believed to contain hydroxy and/orcarboxylic acid groups. Many of these commercially available AdhesionPromoters are derived from diols and polyols which are In esterified byreaction with (meth)acrylate acid and consequently they may contain free(meth)acrylic acid. This free (meth)acrylic acid may be the actualAdhesion Promoter. However, for the purpose of the invention commercialmixtures containing free (meth)acrylic acid are to be regarded as singlecompounds, especially regarding their acid values.

The carboxy containing monomers may exhibit acid values in excess of 300mg KOH/g such as (meth)acrylic acid. However, it is preferred to usecarboxy containing monomers where the acid value is not greater than120, more preferably not greater than 80 and especially not greater than30 mg KOH/g.

When the ink jet ink contains a metal adhesion promoting compound whichcontains a carboxylic acid group it may be preferred to make the inkavailable in a two-pack composition in order to improve stability understorage. In a preferred two-pack composition, the initiator (componentC) and carboxy containing metal adhesion promoting compound (componentB) are separated. In a particularly preferred two-pack composition, theinitiator is made available in a formulation together with either someor all of the acrylate functional monomers which constitute component(A), especially the mono-functional acrylate monomers.

It is preferred that the amount of metal adhesion promoting organiccompound which is component B) in the solder mask ink is not less than0.25 and especially not less than 0.4 parts. Preferably the amount ofmetal adhesion promoting organic compound is not greater than 20 parts,more preferably not greater than 15 parts and especially not greaterthan 10 parts.

After polymerisation of the solder mask ink the solder mask shouldexhibit high resistance to alkali and have high resistivity.Consequently, it is preferred that the acid value of the total soldermask ink and hence the resultant solder mask is not greater than 30,more preferably not greater than 20 and especially not greater than 10mg KOH/g.

The initiator represented by component C) may be any initiator includingoptional synergists which are commonly used in the trade to initiatepolymerisation of acrylate functional monomers. The initiator andsynergist when present are preferably free-radical initiators and may beactivated by actinic radiation such as UV radiation or by acceleratedparticles as, for example, in electron beam radiation. Suitable sourcesof actinic radiation include mercury lamps, xenon lamps, carbon arclamps, tungsten filament lamps, lasers, electron beam and sunlight.Ultraviolet (UV) radiation is especially that emitted by medium pressuremercury lamps. Thus the initiator is preferably a photo-initiator.

Examples of suitable initiators and synergists are anthraquinone,substituted anthraquinones such as alkyl and halogen substitutedanthraquinones such as 2-tert butyl anthraquinone,1-chloroanthraquinone, p-chloroanthraquinone, 2-methylanthraquinone,2-ethylanthraquinone, octamethyl anthraquinone and 2-amylanthraquinone;optionally substituted polynuclear quinones such as-1,4-naphthoquinone,9,10-phenanthraquinone, 1,2-benzanthraquinone, 2,3-benzanthraquinone,2-methyl-1,4-naphthoquinone, 2,3-dichloronaphthoquinone,1,4-dimethylanthraquinone, 2,3-dimethylanthraquinone,2-phenylanthraquinone, 2,3-diphenylanthraquinone,3-chloro-2-methylanthraquinone, retenequinone,7,8,9,10-tetrahydronapthaacenequinone, 1,2,3,4-tetrahydrobenzanthracene-7.2-dione, acetophenones such as acetophenone,2,2-dimethyoxy-2-phenyl acetophenone, 2,2-diethoxy-2-phenylacetophenone, 1,1-dichloro acetophenone, 1-hydroxycyclohexyl-phenylketone and 2-methyl-1-(4methylthio)phenyl-2-morpholin-propan-1-one; thioxanthones such as2-methylthioxanthone, 2-decylthioxanthone, 2-dodecylthioxanthone,2-isopropylthioxanthone, 2,4-dimethylthioxanthone,2,4-diethylthioxanthone, 2-chlorothioxanthone and2,4-diisopropylthioxanthone; ketals such as acetophenone dimethylketaland dibenzylketal; benzoins and benzoin alkyl ethers such as benzoin,benzyl benzoin methyl ether, benzoin isopropyl ether and benzoinisobutyl ether; azo compounds such as azobisisovaleronitrile;benzophenones such as benzophenone, methylbenzophenone,4,4¹-dichlorobenzophenone, 4,4¹-bis-diethylaminobenzophenone, Michler'sketone and xanthones, including mixtures thereof. Important commercialinitiators and synergists are Speedcure™ ITX, EHA and 3040, Irgacure™184, 369, 907 and 1850 and Daracure™ 1173. Speedcure™, Irgacure™ andDaracure™ are registered trademarks of Lambson Plc and Ciba GmbH,respectively.

The amount of initiator and synergist is preferably not greater than 20parts and more preferably not greater than 15 parts and especially notgreater than 12 parts by weight. It is also preferred that the amount ofinitiator is not less than 5 parts.

The solder mask ink may be exposed to actinic radiation and/or particlebeam radiation at any convenient time after the ink is expressed from anink jet printing nozzle of a print head and includes in-flight andpost-flight exposure of the ink.

The thermal treatment to which the solder mask may be exposed afterexposure to actinic or particle beam radiation is preferably carried outat a temperature of from 80° C. to 250° C. It is preferred that thetemperature is not less than 100° C. and especially not less than 120°C. In order to inhibit charring of the solder mask the temperature ispreferably not greater than 200° C. and especially not greater than 160°C. Thermal treatment is normally carried out for between 15 and 90minutes. The purpose of the thermal treatment is to increase thepolymerisatlon of the solder mask. This further polymerisation duringthermal treatment may be accelerated by including radical initiatorswhich promote thermal curing of polymers such as peroxides and azocompounds. However, the addition of such thermal curing initiators isnot generally necessary since the polymeric solder mask normally retainssufficient free radicals following exposure of the solder mask ink toactinic or particle beam radiation.

The metal, circuitry of the electronic device may be any metal or alloywhich is conventionally used for such devices and includes gold, silver,palladium, nickel/gold, nickel, tin, tin/lead, aluminium, tin/aluminiumand especially copper.

The dielectric substrate of the electronic device may be anynon-conductive material but it is typically paper/resin composite or aresin/fibre glass composite, ceramic, polyester or polyimide (e.g.Kapton of DuPont Inc).

The polymer or prepolymer which is component D) may be any polymericmaterial which is compatible with the acrylic functional monomersrepresented by component A). It is distinguished from the acrylatefunctional monomers represented by A) in that it is devoid of acrylatefunctionality and/or is derived from polymerising one or more acrylatefunctional monomers. The polymer or prepolymer typically has a numberaverage molecular weight of from 500 to about 100,000.

Preferably the molecular weight is not greater than 30,000 andespecially not greater than 10,000. It is also preferred that themolecular weight is not less than 700 and especially not less than2,000. The polymeric material may belong to any class of resin such aspolyurethane, polyester, polyimide, polyamide, epoxy,silicone-containing resin or fluorinated resin materials, includingmixtures thereof. The prepolymer or polymer may react with one or moreof the acrylate functional monomers represented by component A) or itmay intercolate with the acrylate polymer formed by polymerising theacrylate monomers represented by component A). It is preferred that theamount of component D) when present is not greater than 10 parts, morepreferably not greater than 5 parts and especially not greater than 3parts by weight. It is especially preferred that the ink is free fromcomponent D).

Although the solder mask ink may be colourless it is generally preferredto include a colorant since this more clearly identifies those regionsof the electronic device to which the solder mask has been applied.

The colorant which is component E) of the solder mask ink composition ispreferably a pigment and may be organic or inorganic including thosepigments with surface modification which facilitates self dispersion inthe ink. The pigment may be from any of the recognised classes ofpigments described, for example, in the Third Edition of the ColourIndex (1971) and subsequent revisions of and supplements thereto underthe chapter headed “Pigments”. Examples of inorganic pigments aretitanium dioxide, Prussian blue, cadmium sulphide, iron oxides,vermillion, ultramarine and the chrome pigments, including chromates,molybates and mixed chromates and sulphates of lead, zinc, barium,calcium and mixtures and modifications thereof which are commerciallyavailable as greenish-yellow to red pigments under the names primrose,lemon, middle, orange, scarlet and red chromes. Examples of organicpigments are those from the azo, diazo, condensed azo, thioindigo,indanthrone, isoindanthrone, anthanthrone, anthraquinone,isodibenzathrone, triphendioxazine, quinacridone and phthalocyanineseries, especially copper phthalocyanine and its nuclear halogenatedderivatives, and also lakes of acid, basic and mordant dyes. Carbonblack, although strictly inorganic, behaves more like an organic pigmentin its dispersing properties. Preferred organic pigments arephthalocyanines, especially copper phthalocyanines, monoazos, diazos,indanthrones, anthanthrones, quinacridones and carbon blacks.

As noted hereinbefore, the solder mask ink jet composition is of use inthe manufacture of electronic devices comprising a dielectric substrateand electrically conductive circuitry such as PCB's. In this industrialsector the preferred colour is blue or green. The blue pigment ispreferably one of the phthalocyamine series. Examples of blue pigmentsare C.I. Pigment Blue 1, 15, 15:1, 15:2, 15:3, 15:4, 15:6, 16, 24 and60. Green pigments are generally a mixture of blue and yellow or orangepigments or may be green pigments per se such as halogenatedphthalocyanines, for example copper or nickel brominated phthalocyanine.

The pigment is typically incorporated into the solder mask ink jetcomposition by milling it together with one or more of the acrylatefunctional monomers in the presence of a dispersant. The dispersant ispreferably a polyester/polyamine and is, for example, a dispersant asdisclosed in U.S. Pat. No. 6,197,877. Dispersants of this type areavailable under the trademark Solsperse dispersants (Avecia Ltd). Thedispersant may also include a synergist such as a quaternary ammoniumsalt of a partially sulphonated copper phthalocyanine pigment. Examplesof such synergists are disclosed in GB-A-1508576, GB-A-2108143 and WO01/14479 and are available under the Solsperse™ trademark.

The ratio of dispersant to synergist is typically from 1:1 to 10:1 byweight and is preferably about 5:1 by weight. The total amount ofdispersant and synergist to pigment may vary over wide limits and istypically from 50% to 150% by weight relative to the weight of colorant.The amount of colorant in the solder mask ink is preferably not greaterthan 5 parts, more preferably not greater than 3 parts and especiallynot greater than 2 parts by weight.

The surfactant which is component F) of the solder mask ink compositionwhen present may be any surface-active material which aids thehomogeneity of the ink composition and provides desirable surfacetension and wetting properties to the resultant ink. The surfactant mayalso be selected to adjust the viscosity of the ink composition to thedesired limits. It is preferably anionic and especially non-ionic. It isalso preferably aliphatic in nature, optionally containing silicon atomsand/or fluorine. The surfactant is preferably reactive with the acrylatemonomers (component A)) and it is especially preferred that it containsone or more (meth)acrylate functional groups as defined hereinbefore.Examples of organic silicon acrylate surfactants are polysiliconescontaining repeat units of formula —Si(R′,R′)—O— where R′ is monovalenthydrocarbyl which may be ethyl or aryl and also at least one group offormula —Si(X,R′)—O— where X is a (meth)acrylate moiety. Specificexamples are Tegorad™ 2200N and 2100 of Tego Chemie.

The solder mask ink preferably has a surface tension of from 20 to 40and especially between 25 and 35 mN/m. Consequently, the amount ofsurfactant is generally from 0.1 to 0.6 parts by weight.

As will be understood from the term “comprises” the solder mask ink maycontain further components in addition to components A) to F) which arecommonly used in actinic radiation or particle beam curablecompositions. Such adjuvants include slip modifiers, thixotropic agents,foaming agents, anti-foaming agents, waxes, oils, plasticisers, binders,antioxidants, photo-initiator stabilisers, gloss agents, fungicides,bactericides, organic and/or inorganic filler particles, levellingagents, opacifiers and antistatic agents. In a further embodiment thesolder mask ink consists essentially of components A) to F) and in astill further embodiment the solder mask ink consists of components A)to F).

The solder mask ink may be prepared by any method known to the art ofactinic radiation or particle beam curable compositions. Typically, thecomponents A) and B) are mixed together with rapid stirring at atemperature from 20 to 60° C., preferably under reduced lightconditions, until a homogenous solution is obtained. Component C) isthen added and stirring continued at 20 to 60° C. under reduced lightconditions. Finally, optional components D), E) and F) are added.

As noted hereinbefore component E) is preferably a pigment, especially ablue pigment and is preferably prepared by any suitable attritionprocess such as grinding, pebble or bead milling the pigment togetherwith dispersant in the presence of small amounts of component A). Whencomponent E) is a pigment it is added to the other components of the inkis a pre-dispersed form.

The ink composition is then preferably filtered at 20 to 25° C. toremove any particulate matter. Filtration may include a process known ascascade filtration when the ink composition passes through successivelyfiner filter media, for example, 10, 6, 4.5, 2.5 and 1.2 micron filters.

In one embodiment the solder mask ink is not removed from the substrateusing alkali.

As noted hereinbefore the process according to the invention is mainlyconcerned with the manufacture of printed circuit boards. Afterpolymerisation of the solder mask ink by actinic or particle beamradiation and optionalthermal curing the cured ink preferably exhibitsthe following properties both individually and collectively:

-   -   Good adhesion to a dielectric substrate with electrically        conductive metal or alloy circuitry for a solder mask coating of        from 10 to 30 μm thickness as determined using ASTR test method        D3359-87.    -   The polymerised solder mask withstands molten for at least 10        seconds at 200° C. and especially at 260° C. according to IPC        test method 3.7.2 of IPC-SM-840C.    -   Pencil hardness for a 10 to 30 μm thick film of not less than F        and especially not less than 3H as determined using IPC test        method TR 2.4.27.2 of IPC-TM-650.    -   Withstand dielectric breakdown of not less than 500 volts/25 μm        film thickness as determined by IPC test method TR 2.5.6.1 of        IPC-SM-840C.    -   Surface resistivity between adjacent electrically conductive        tracks of the circuitry which is not less than 5×10⁹ ohms as        determined by test method 2.6.3.1 of IPC-SM-840C.

As noted hereinbefore, the process according to the invention isparticularly suited for making PCB's, especially wherein theelectrically conductive circuitry is copper. Thus, according to afurther aspect of the invention, there is provided an electronic devicecomprising a dielectric substrate containing electrically conductivemetal circuitry and a solder mask which has been prepared using theprocess as described hereinbefore.

Some of the solder mask inks used in the process of the invention form afurther feature of the present invention. Thus, according to a furtheraspect of the invention, there is provided a non-aqueous solder mask inkwhich is substantially free from organic solvents which comprises thefollowing components:

-   -   A) 30 to 90 parts acrylate functional monomers which are mono or        higher acrylate functional monomers comprising from 5-95% by        weight of one or more monofunctional monomers;    -   B) 0.1 to 30 parts metal adhesion promoting organic compound;    -   C) 5 to 30 parts initiator;    -   D) 0 to 10 parts polymer and/or prepolymer;    -   E) 0 to 5 parts colorant;    -   F) 0 to 5 parts surfactant; and        wherein the ink has a viscosity of not greater than 30 cPs        (mPa.s) at 40° C. and all parts are by weight.

According to a still further aspect of the invention there is provided anon-aqueous solder mask ink which is substantially free from organicsolvents which comprises:

-   -   A) 30 to 90 parts acrylate functional monomers which are mono or        higher acrylate functional monomers comprising. 5-95% by weight        of one or more mono-functional monomers;    -   B) 0.1 to 30 parts metal adhesion promoting organic compound        containing one or more carboxylic acid groups and having an acid        value of not greater than 120 mg KOH/g;    -   C) 5 to 30 parts initiator;    -   D) 0 to 10 parts polymer and/or prepolymer;    -   E) 0 to 5 parts colorant;    -   F) 0 to 5 parts surfactant;        wherein the ink has a viscosity of not greater than 20 cPs        (mPa.s) at 40° C. and all parts are by weight.

Preferably the metal adhesion promoting organic compound containing oneor more carboxylic acid groups has an acid value of not greater than 30mg KOH/g.

According to a further aspect of the invention there is provided anon-aqueous solder mask ink which is substantially free from organicsolvents which comprises the components:

-   -   A) 30 to 90 parts acrylate functional monomers which are mono or        higher acrylate functional monomers comprising 5-95% by weight        of one or more mono-functional monomers;    -   B) 0.1 to 30 parts metal adhesion promoting organic compound        containing one or more carboxylic acid groups;    -   C) 5 to 30 parts initiator;    -   D) 0 to 10 parts polymer and/or prepolymer;    -   E) 0 to 5 parts colorant;    -   F) 0 to 5 parts surfactant; and        wherein the acid value of the total solder mask ink is not        greater than 30 mg KOH/g and all parts are by weight.

In one embodiment of the above inks the number of parts of componentsA)+B)+C)+D)+E)+F)=100.

The solder mask inks may also be used for printing legends ontoelectronic devices and are particularly well suited to printing ontopolyacrylate solder masks, especially following exposure to actinic orparticle beam (electron) radiation and optionally prior to thermaltreatment.

The solder mask inks of the present invention may of course containfurther components (other than trace amounts of water and organicsolvents) in addition to components A) to F) specified above, forexample preservatives, biocides, rheology modifiers, surfactants,levelling agents, antifoaming agents, anti-kogation agents andcombinations thereof. The solder mask inks are generally made availableto the manufacturer of electronic devices in the form of replacementcartridges for ink jet printers. Hence, according to a further aspect ofthe invention, there is provided a cartridge for an ink jet printercomprising a chamber and an ink wherein the ink is present in thechamber and the ink is a solder mask ink as described hereinbefore.

The present invention also provides an electronic device obtained by aprocess according to the present invention.

The invention is further illustrated by the following examples whereinall references are to parts by weight unless expressed to the contrary.

EXAMPLES 1 TO 74

The acrylate monomers and metal adhesion promoter were mixed by stirringat 25° C. for about 1 hour to give a homogeneous solution. The initiatorwas then added under reduced light conditions and the mixture stirred at60° C. to dissolve the initiator. The mixture was then cooled to 25° C.and the surfactant was added with stirring.

The pigment and dispersant were milled for 16 hours at 25° C. in thepresence of a small amount of acrylate monomers and adhesion promoterand 3 mm diameter balatini glass beads using a horizontal shaker. Thebeads were then removed and the pigment dispersion was added to theabove mixture. The resulting ink was then filtered using a cascadeseries of filters with pore sizes of 10, 6, 4.5, 2.5 and 1.2 μ.

The composition of the solder mask ink is detailed in Table 1 below.

The following ink properties were determined as follows:

Viscosity was measured at 40° C. using a Brookfield Viscometer equippedwith a number 18 spindle rotating at 100 rpm.

Surface tension was measured at 25° C. using a DuNouy ring.

Ink jet start up and firing was assessed using a Spectra Galaxy 30 plprint head and the results assessed as good, moderate or poor.

The solder mask ink was then applied to an uncoated dielectric FR4 boardlaminated with 30 μm copper sheet to a thickness of 25 mm either using aK-bar or block printing with a Spectra Galaxy ink jet printer. Thesolder mask was then cured by passing a UV 'Fusion D bulb” running at120 W/cm with energy output of 300-900 MJ/cm (or 2.8-3.6 W/cm² at a passspeed of 10-35 m/min. After UV curing, the solder mask ink was thermallycured by heating for 60 min in a fan oven at 150° C.

The following properties of the cured solder mask ink were measured asfollows:

Pencil harness using IPC test method TM 2.4.27.2 of IPC-TM-650.

Adhesion using ASTM test method D3359-87 both before and after thermalcuring and quantified as good, moderate or poor.

Resistance to hot solder in a solder bath heated to 260° C. for 10seconds using IPC test method 3.7.2. of IPC-SM-840C.

Dielectric breakdown voltage using IPC test method TM 2.5.6.1 ofIPC-TM-650.

Resistance to solvents using IPC test method 3.6.1.1 of IPC-SM-840C.

The results were given in Table 2 below. TABLE 1 Expressed in parts byweight. Example Component Ink 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Acrylate Monomers 1 Sartomer ™ 506 38.2 36.2 34.2 2 Sartomer ™ 306 23.023.0 23.0 3 Actilane ™ 430 12.5 12.5 12.5 4 Actilane ™ 251 12.5 12.512.5 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 5Actilane ™ 440 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.0 15.015.0 6 Actilane ™ 425 58.2 56.2 53.2 53.2 53.2 15.0 15.0 15.0 15.0 15.015.0 15.0 7 Photomer ™ 4072 8 Photomer ™ 4039 9 Hexanediol diacrylate 102-Hydroxyethyl methacrylate 11 Lauryl acrylate 12 Isodecyl acrylate 13Sartomer ™ 238 14 Actilane ™ 411 15 Actilane ™ 422 16 Actilane ™ 440 17Actilane ™ 441 Adhesion Promoters 18 2-acrylamidoglycolic acidmonohydrate 19 Mono-2-(methacryloyloxy)ethyl phthalate 20 Acrylic acid2.0 4.0 6.0 21 Actilane ™ 276 5.0 22 Actilane ™ 32HD20 5.0 23 Actilane ™340 5.0 5.0 5.0 24 Actilane ™ 505 5.0 25 Aceto acetoxyethyl methacrylate26 Photomer ™ 5429 27 Actilane ™ 820 2.0 5.0 5.0 5.0 28 Actilane ™ 8725.0 29 Actilane ™ 890 30 Photomer ™ 5004F 31 Sartomer ™ 9050 32Mono-2-(methacryloyloxy) ethyl succinate 33 Bis(2-methacryloyloxy) ethylphosphate 34 Photomer ™ 4703 35 2-Hydroxy-3-phenoxypropyl acrylate 36Diurethane dimethacrylate Initiator 37 Speedcure ™ 3040 10.0 10.0 10.010.0 10.0 10.0 10.0 10.0 10.0 38 Speedcure ™ ITX 2.0 2.0 2.0 2.0 2.0 2.039 Speedcure ™ EHA 4.0 4.0 4.0 4.0 4.0 4.0 40 Speedcure ™ DETX 41Irgacure ™ 369 4.0 4.0 4.0 4.0 4.0 4.0 42 Irgacure ™ 907 43 Irgacure ™1173 44 Irgacure ™ 1850 45 Benzophenone Surfactant 46 Tegorad ™ 2200N0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Colourant 47Irgalite ™ Blue GLVO 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.50.5 0.5 48 Pallotol ™ Yellow 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.40.4 0.4 0.4 0.4 D1819 Dispersant 49 Solsperse ™ 0.5 0.5 0.5 0.5 0.5 0.50.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 0.5 dispersant Example Component Ink 1617 18 19 20 21 22 23 24 25 26 27 28 29 30 Acrylate Monomers 1 Sartomer ™506 38.2 23.4 20.4 15.4 28.4 28.4 40.0 38.2 43.0 21.9 0.6 20.6 1.3 35.335.3 2 Sartomer ™ 306 23.0 24.0 22.9 1.3 0.6 0.6 1.3 1.3 20.9 20.9 3Actilane ™ 430 20.0 20.0 20.0 12.5 12.5 11.8 5.6 19.6 20.0 20.0 20.020.0 11.4 11.4 4 Actilane ™ 251 15.0 20.0 20.0 20.0 12.5 12.5 11.8 11.219.6 20.0 20.0 20.0 20.0 11.4 11.4 5 Actilane ™ 440 15.0 6 Actilane ™425 15.0 18.0 16.0 11.0 23.0 7 Photomer ™ 4072 8 Photomer ™ 4039 9Hexanediol diacrylate 10 2-Hydroxyethyl methacrylate 11 Lauryl acrylate12 Isodecyl acrylate 13 Sartomer ™ 238 21.3 42.6 21.3 40.6 14 Actilane ™411 15 Actilane ™ 422 5.4 16 Actilane ™ 440 17 Actilane Actilane ™ 441Adhesion Promoters 18 2-acrylamidoglycolic acid monohydrate 19Mono-2-methacryloyloxy) ethyl phthalate 20 Acrylic acid 4.8 21 Actilane276 22 Actilane 32HD20 23 Actilane 340 24 Actilane 505 25 Acetoacetoxyethyl 5.0 10.0 20.0 10.0 10.0 methacrylate 26 Photomer 5429 9.127 Actilane 820 28 Actilane 872 29 Actilane 890 5.0 30 Photomer 5004F9.1 31 Sartomer 9050 4.9 5.0 5.0 5.0 5.0 32 Mono-2-methacryloyloxy)ethyl succinate 33 Bis(2-methacryloyloxy) ethyl phosphate 34 Photomer4703 35 2-Hydroxy-3- phenoxypropyl acrylate 36 Diurethane dimethacrylateInitiator 37 Speedcure 3040 10.0 10.0 10.0 10.0 10.0 10.0 38 SpeedcureITX 1.9 1.8 2.0 2.0 2.0 2.0 2.0 1.8 1.8 39 Speedcure EHA 3.8 3.6 3.9 4.04.0 4.0 4.0 3.6 3.6 40 Speedcure DETX 41 Irgacure 369 3.8 3.6 3.9 4.04.0 4.0 4.0 3.6 3.6 42 Irgacure 907 43 Irgacure 1173 44 Irgacure 1850 45Benzophenone Surfactant 46 Tegorad 2200N 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.40.4 0.4 0.4 0.4 0.4 0.4 0.4 Colourant 47 Irgalite Blue 0.5 1.0 1.0 1.01.0 1.0 1.0 0.9 0.5 0.3 0.3 0.5 0.5 0.9 0.9 GLVO 48 Paliotol Yellow 0.41.0 1.0 1.0 1.0 1.0 0.7 0.7 0.4 0.2 0.2 0.4 0.4 0.7 0.7 D1819 Dispersant49 Solsperse 0.5 1.2 1.2 1.2 1.2 1.2 1.0 0.9 0.5 0.3 0.3 0.5 0.5 0.9 0.9dispersant Example Component Ink 31 32 33 34 35 36 37 38 39 40 41 42 4344 45 Acrylate Monomers 1 Sartomer 506 36.9 39.8 37.9 37.0 37.0 35.335.3 37.0 1.3 1.3 35.3 33.8 31.1 42.1 54.3 2 Sartomer 306 21.2 0.0 22.421.9 21.9 20.9 20.9 21.9 24.3 24.3 20.9 20.0 18.4 1.3 0.6 3 Actilane 43011.5 19.9 12.2 11.9 11.9 11.4 11.4 11.9 12.5 12.5 11.4 10.9 10.0 19.914.6 4 Actilane 251 11.5 19.9 12.2 11.9 11.9 11.4 11.4 11.9 12.5 12.511.4 10.9 10.0 19.9 14.6 5 Actilane 440 6 Actilane 425 7 Photomer 4072 8Photomer 4039 9 Hexanediol 27.6 27.6 diacrylate 10 2-Hydroxyethylmethacrylate 11 Lauryl acrylate 4.5 5.0 12 Isodecyl acrylate 4.5 5.0 4.58.7 16.0 13 Sartomer 238 14 Actilane 411 15 Actilane 422 16 Actilane 44017 Actilane 441 Adhesion Promoters 18 2-acrylamidoglycolic acidmonohydrate 19 Mono-2- (methacryloyloxy)ethyl phthalate 20 Acrylic acid21 Actilane 276 22 Actilane 32HD20 23 Actilane 340 24 Actilane 505 25Aceto acetoxyethyl methacrylate 26 Photomer 5429 9.2 10.0 2.4 4.8 4.84.5 4.5 4.8 5.0 5.0 4.5 4.3 4.0 5.0 4.9 27 Actilane 820 28 Actilane 87229 Actilane 890 30 Photomer 5004F 31 Sartomer 9050 32Mono-2-(methacryloyloxy) ethyl succinate 33 Bis(2-methacryloyloxy) ethylphosphate 34 Photomer 4703 35 2-Hydroxy-3-phenoxypropyl acrylate 36Diurethane dimethacrylate Initiator 37 Speedcure 3040 9.2 10.0 38Speedcure ITX 2.0 1.9 1.9 1.8 1.8 1.9 2.0 2.0 1.8 1.7 1.6 2.0 2.0 39Speedcure EHA 3.9 3.8 3.8 3.6 3.6 3.8 4.0 4.0 3.6 3.5 3.2 4.0 3.9 40Speedcure DETX 41 Irgacure 369 3.9 3.8 3.8 3.6 3.6 3.8 4.0 4.0 3.6 3.53.2 4.0 3.9 42 Irgacure 907 43 Irgacure 1173 44 Irgacure 1850 45Benzophenone Surfactant 46 Tegorad 2200N 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.40.4 0.4 0.4 0.3 0.3 0.4 0.4 Colourant 47 Irgalite Blue GLVO 0.0 0.0 1.01.0 1.0 0.9 0.9 1.0 0.5 0.5 0.9 0.9 0.8 0.5 0.2 48 Paliotol Yellow 0.00.0 0.7 0.7 0.7 0.7 0.7 0.7 0.4 0.4 0.7 0.7 0.6 0.4 0.2 D1819 Dispersant49 Solsperse dispersant 0.0 0.0 1.0 1.0 1.0 0.9 0.9 1.0 0.5 0.5 0.9 0.90.8 0.5 0.3 Example Component Ink 46 47 48 49 50 51 52 53 54 55 56 57 5859 60 Acrylate Monomers 1 Sartomer 506 54.3 63.1 54.3 23.1 23.1 9.4 9.455.0 54.2 61.7 63.6 63.6 63.6 63.6 63.6 2 Sartomer 306 15.3 15.3 29.235.8 0.6 44.6 0.6 13.6 13.0 13.8 13.0 13.0 13.0 13.0 13.0 3 Actilane 4307.3 2.9 12.7 12.7 15.1 15.1 7.5 7.3 3.2 3.6 3.6 3.6 3.6 3.6 4 Actilane251 7.3 2.9 12.7 12.7 15.1 15.1 7.5 7.3 3.2 3.6 3.6 3.6 3.6 3.6 5Actilane 440 6 Actilane 425 7 Photomer 4072 8 Photomer 4039 9 Hexanedioldiacrylate 35.2 43.9 10 2-Hydroxyethyl methacrylate 11 Lauryl acrylate12 Isodecyl acrylate 13 Sartomer 238 14 Actilane 411 15 Actilane 422 16Actilane 440 17 Actilane 441 Adhesion Promoters 18 2-acrylamidoglycolicacid monohydrate 19 Mono-2- (methacryloyloxy) ethyl phthalate 20 Acrylicacid 21 Actilane 276 22 Actilane 32HD20 23 Actilane 340 24 Actilane 50525 Aceto acetoxyethyl methacrylate 26 Photomer 5429 4.9 4.9 4.9 4.9 4.94.9 4.9 5.0 5.0 5.0 4.8 4.8 4.8 4.8 4.8 27 Actilane 820 28 Actilane 87229 Actilane 890 30 Photomer 5004F 31 Sartomer 9050 32 Mono-2-(methacryloyloxy) ethyl succinate 33 Bis(2-methacryloyloxy) ethylphosphate 34 Photomer 4703 35 2-Hydroxy-3- phenoxypropyl acrylateInitiator 37 Speedcure 3040 38 Speedcure ITX 2.0 2.0 2.0 2.0 2.0 2.0 2.02.0 2.0 2.0 2.0 2.0 2.0 39 Speedcure EHA 3.9 3.9 3.9 3.9 3.9 3.9 3.9 4.04.0 4.0 4.0 4.0 4.0 4.0 4.0 40 Speedcure DETX 2.0 41 Irgacure 369 3.93.9 3.9 3.9 3.9 3.9 3.9 4.0 4.0 4.0 4.0 4.0 4.0 42 Irgacure 907 4.0 43Irgacure 1173 4.0 44 Irgacure 1850 45 Benzophenone 2.0 Surfactant 46Tegorad 2200N 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.40.4 Colourant 47 Irgalite Blue GLVO 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.4 1.01.0 0.4 0.4 0.4 0.4 0.4 48 Paliotol Yellow 0.2 0.2 0.2 0.2 0.2 0.2 0.20.3 0.8 0.7 0.3 0.3 0.3 0.3 0.3 D1819 Dispersant 49 Solsperse dispersant0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.4 1.0 1.0 0.4 0.4 0.4 0.4 0.4 ExampleComponent Ink 61 62 63 64 65 66 67 68 69 70 71 72 73 74 Control AcrylateMonomers 1 Sartomer 506 63.6 63.6 63.6 63.6 53.4 63.4 58.4 63.4 62.863.3 58.3 63.3 58.3 58.4 40.2 2 Sartomer 306 13.0 13.0 13.0 13.0 13.013.0 13.0 13.0 14.5 13.2 13.2 13.2 13.2 13.0 23.0 3 Actilane 430 3.6 3.63.6 3.6 3.6 3.6 3.6 3.6 3.2 3.6 3.6 3.6 3.6 3.6 12.5 4 Actilane 251 3.63.6 3.6 3.6 3.6 3.6 3.6 3.6 3.2 3.6 3.6 3.6 3.6 3.6 12.5 5 Actilane 4406 Actilane 425 7 Photomer 4072 8 Photomer 4039 9 Hexanediol diacrylate10 2-Hydroxyethyl methacrylate 11 Lauryl acrylate 12 Isodecyl acrylate13 Sartomer 238 14 Actilane 411 15 Actilane 422 16 Actilane 440 17Actilane 441 Adhesion Promoters 18 2-acrylamidoglycolic acid 5.0 10.0monohydrate 19 Mono-2- 5.0 10.0 (methacryloyloxy)ethyl phthalate 20Acrylic acid 21 Actilane 276 22 Actilane 32HD20 23 Actilane 340 24Actilane 505 25 AAEM 26 Photomer 5429 4.8 4.8 4.8 4.8 5.0 27 Actilane820 28 Actilane 872 29 Actilane 890 30 Photomer 5004F 31 Sartomer 905032 Mono-2-methacryloyloxy) ethyl succinate 33 Bis(2-methacryloyloxy)15.0 ethyl phosphate 34 Photomer 4703 35 2-Hydroxy-3- 5.0 10.0phenoxypropyl acrylate 36 Diurethane 5.0 10.0 dimethacrylate Initiator37 Speedcure 3040 10.0 38 Speedcure ITX 4.0 2.0 2.0 2.0 2.0 2.0 2.0 2.02.0 2.0 2.0 2.0 39 Speedcure EHA 6.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.0 4.04.0 4.0 40 Speedcure DETX 41 Irgacure 369 10.0 4.0 4.0 4.0 4.0 4.0 4.04.0 4.0 4.0 4.0 4.0 42 Irgacure 907 43 Irgacure 1173 5.0 44 Irgacure1850 5.0 45 Benzophenone Surfactant 46 Tegorad 2200N 0.4 0.4 0.4 0.4 0.40.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 Colourant 47 Irgalite Blue GLVO0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.5 48 PaliotolYellow D1819 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.1 0.1 0.1 0.1 0.1 0.3 0.4Dispersant 49 Solsperse dispersant 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.4 0.40.4 0.4 0.4 0.4 0.4 0.5

TABLE 2 Property Example 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 Viscosity @40° C. (cP) ST(mN/m) Pencil Hardness (uv) H 3H 4H 4H 4H 3H 3H HB 3H 2H HHB F HB Adhesion on copper (uv) 0 1 5 4 4 2 0 1 5 3 1 0 0 0 PencilHardness 3H 4H 5H 5H 5H (uv + bake) Adhesion on copper 3 5 5 5 5 (uv +bake) Ink jet performance Solder bath test Dielectric breakdown voltage(KV/mil) Solvent resistance 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30Viscosity @ 40° C. (cP) 12.8 13.5 13.0 13.3 9.0 12.7 20.0 16.3 14.6ST(mN/m) 26.5 25.0 24.0 Pencil Hardness (uv) F HB HB F HB 2H 4-5H 5-6H4H 2-3H F Adhesion on copper (uv) 0 0 0 0 0 0 4 Pencil Hardness F H 4H4H 4H 6H 6H 6H 5-6H F-2H (uv + bake) Adhesion on copper 4 4 5 5 4 3 3 3(uv + bake) Ink jet performance Good Solder bath test Pass Pass PassPass Dielectric breakdown voltage (KV/mil) Solvent resistance 31 32 3334 35 36 37 38 39 40 41 42 43 44 45 Viscosity @ 40° C. (cP) 10.7ST(mN/m) 29.0 Pencil Hardness (uv) 3-4H 2H 4H 3-4H F.Fail 2-3H 2HAdhesion on copper (uv) Pencil Hardness 5H 2H 5H 4-5H 5-6H 5-6H 5-6H5-6H 5-6H 4-5H 4-5H 4-5H 6H 5-6H (uv + bake) Adhesion on copper 4 4(uv + bake) Ink jet performance Solder bath test Dielectric breakdownvoltage (KV/mil) Solvent resistance 46 47 48 49 50 51 52 53 54 55 56 5758 59 60 Viscosity @ 40° C. (cP) 10.7 9.0 8.0 13.7 10.0 16.4 9.8 9.8 8.2ST(mN/m) 28.5 27.0 27.0 27.0 28.0 27.0 27.0 27.5 28.5 27.3 PencilHardness (uv) 5H 4-5H 4H 2H 3-4H F-2H F-2H 4H 6H H H H 2H H Adhesion oncopper (uv) 4 4 4 4 4 4 4 Pencil Hardness 6H 6H 6H 6H 6H 5H 5H 6H 6H 6H3H 2H 2H 5H H (uv + bake) Adhesion on copper 4 4 4 4 4 4 4 4 4 4 4 4 4 55 (uv + bake) Ink jet performance Solder bath test Pass Pass Pass PassPass Pass Pass Dielectric breakdown 3.2 3.5 voltage (KV/mil) Solventresistance 61 62 63 64 65 66 67 68 69 70 71 72 73 74 Control Viscosity @40° C. (cP) ST(mN/m) Pencil Hardness (uv) H H H 2H 3H 3H 4H F F F F 3H FAdhesion on copper 4 4 4 3 4 4 4 4 0 (uv) Pencil Hardness H 2H 2H 2H 3H3H 5H 4H 4H 4H 4H 3H F (uv + bake) Adhesion on copper 4 5 5 5 4 4 5 4 0(uv + bake) Ink jet performance Good Solder bath test Pass Pass PassPass Pass Pass Pass Pass Pass Pass Pass Pass Fail Dielectric breakdownvoltage (KV/mil) Solvent resistance Pass

1. A process for making an electronic device which comprises applying anon-aqueous solder mask ink which is substantially free from organicsolvent to a dielectric substrate containing electrically conductivemetal circuitry, exposing the solder mask ink to actinic radiationand/or particle beam radiation optionally followed by thermal treatment,whereby the solder mask ink is applied to selected areas of thesubstrate under the control of a computer by ink jet printing andwherein the solder mask ink comprises the components: A) 30-90 partsacrylate functional monomers which are mono or higher acrylatefunctional monomers comprising from 5-95% by weight of one or moremonofunctional monomers; B) 0.1-30 parts metal adhesion promotingorganic compound; C) 0-30 parts initiator; D) 0-10 parts polymer and/orprepolymer; E) 0-5 parts colorant; F) 0-5 parts surfactant; and whereinall parts are by weight:
 2. A process as claimed in claim 1 wherein theviscosity of the solder mask ink is from 8 to 20 cPs (mPa.s) at 40° C.3. A process as claimed in claim 1 wherein the weight average molecularweight of the acrylate functional monomer is not greater than 2,000. 4.A process as claimed in claim 1 wherein the acrylate functional monomeris isobornyl acrylate, tripropylene glycol diacrylate ortrimethylolpropane ethoxylate triacrylate.
 5. A process as claimed inclaim 1 wherein the amount of mono-functional acrylate monomer is 70-95%by weight of the acrylate-functional monomer (component A)).
 6. Aprocess as claimed in claim 1 wherein the adhesion promoter is anacrylate functional monomer.
 7. A process as claimed in claim 1 whereinthe adhesion promoter contains a metal chelant group which is acarboxylic acid.
 8. A process as claimed in claim 7 wherein the adhesionpromoter is (meth)acrylic acid.
 9. A process as claimed in claim 1wherein the adhesion promoter is a polypropylene glycol tetra acrylatecontaining (meth)acrylic acid.
 10. A process as claimed in claim 9wherein the adhesion promoter has an acid value of not greater than 120mg KOH/g.
 11. A process as claimed in claim 1 wherein the amount ofadhesion promoter is not greater than 15 parts by weight. 12-14.(canceled)
 15. A process as claimed in claim 1 wherein the electronicdevice is a printed circuit board.
 16. A process as claimed in claim 1wherein the solder mask ink has an acid value of not greater than 30 mgKOH/g.
 17. (canceled)
 18. A process as claimed in claim 1 wherein theamount of initiator is not less than 5 parts. 19-23. (canceled)
 24. Aprocess as claimed in claim 1 wherein the number of parts of componentsA)+B)+C)+D)+E)+F)=100.
 25. A non-aqueous solder mask ink which issubstantially free from organic solvents which comprises the components:A) 30 to 90 parts acrylate functional monomers which are mono or higheracrylate functional monomers comprising from 5-95% by weight of one ormore monofunctional monomers; B) 0.1 to 30 parts metal adhesionpromoting compound; C) 5 to 30 parts initiator; D) 0 to 10 parts polymerand/or prepolymer; E) 0 to 5 parts colorant; F) 0 to 5 parts surfactant;and wherein the ink has a viscosity of not greater than 30 cPs (mPa.s)at 40° C. and all parts are by weight.
 26. A non-aqueous solder mask inkwhich is substantially free from organic solvents which comprises thecomponents: A) 30 to 90 parts acrylate functional monomers which aremono or higher acrylate functional monomers comprising from 5-95% byweight of one or more monofunctional monomers; B) 0.1 to 30 parts metaladhesion promoting organic compound containing one or more carboxylicacid groups and having an acid value of not greater than 120 mg KOH/gm;C) 5 to 30 parts initiator; D) 0 to 10 parts polymer and/or prepolymer;E) 0 to 5 parts colorant; and F) 0 to 5 parts surfactant; wherein theink has a viscosity of not greater than 30 cPs (mPa.s) at 40° C. and allparts are by weight.
 27. A non-aqueous solder mask ink which issubstantially free from organic solvents which comprises the components:A) 30 to 90 parts acrylate functional monomers which are mono or higheracrylate functional monomers comprising 5-95% by weight of one or moremono-functional monomers; B) 0.1 to 30 parts metal adhesion promotingorganic compound containing one or more carboxylic acid groups; C) 5 to30 parts initiator; D) 0 to 10 parts polymer and/or prepolymer; E) 0 to5 parts colorant; F) 0 to 5 parts surfactant; and wherein the acid valueof the total solder mask ink is not greater than 30 mg KOH/g and allparts are by weight.
 28. An ink as claimed in claims 25, 26 or 27wherein the number of parts of components A)+B)+C)+D)+E)+F)=100.
 29. Acartridge for an ink jet printer comprising a chamber and an ink whereinthe ink is present in the chamber and the ink is a solder mask ink asclaimed in claim
 27. 30. An electronic device obtained by a processaccording to claim 1.